1. Field of the Invention
The invention disclosed and claimed in this application is directed to a torque sensing and control system for a decanter centrifuge. A torque sensor may be incorporated into a known torque control mechanism that will measure the torque acting on a pinion gear of a planetary gearbox used to rotate the centrifuge conveyor and bowl. This data may be used to control various parameters such as the feed rate of the liquid to the separator and vary the speeds of the drive motor for the centrifuge.
2. Description of Related Art
Decanter centrifuges are used in a wide variety of industries to remove fine solids from liquids. In operation, the bowl spins at a high rate of speed creating centripetal force, commonly referred to as G Force, causing the heavier solids to settle to the wall of the bowl. The solids that settle to the wall are conveyed to the solids discharge end of the decanter by the screw conveyor. The screw conveyor is driven by a planetary gearbox in the same direction as the bowl but at a slightly different speed causing a relative differential speed between the bowl and screw conveyor. The planetary gearbox casing or ring gear is connected to the bowl. The planet assembly of the planetary gearbox is connected to the screw conveyor. The pinion shaft of the planetary gearbox is held fixed relative to the base of the centrifuge via the torque arm. The differential speed between the bowl and the screw conveyor is set by the ratio of the planetary gearbox. Common ratios are 50:1 to 175:1. A very common ratio is 53:1 and is widely used by several major manufactures. Common bowl speeds are 1500 rpm to 4000 rpm. A very common speed is 3000 rpm. The resultant screw conveyor differential rpm of a decanter centrifuge operating at 3000 rpm with a 53; 1 planetary gearbox is 3000/53=56.6. The amount of solids that can be conveyed is directly related to the maximum torque of the planetary gearbox. It is common to protect the planetary gearbox from damage due to overloading via a torque control devise connected to the pinion of the planetary gearbox. A very common device is a simple spring loaded over center mechanism which trips at a predetermined load and allows the pinion to rotate at bowl speed, reducing the differential speed to zero and eliminating the load on the planetary gearbox.
In operation the centrifuge is fed the liquid and solids mixture via the centrifuge feed pump. The typical arrangement allows for interconnection of the feed pump motor control with the centrifuge motor control. This arrangement will not allow the feed pump to operate unless the centrifuge is operating normally. This configuration does not have any indication or feedback of the operating load or torque load of the planetary gearbox. Operators rely on experience and manufactures guidelines to determine optimal feed rates. This method of operation is very problematic and inefficient. This is especially true when centrifuging drilling fluid associated with upstream oil and gas exploration. In this application the drilling fluid rheology is constantly changing and so too is the maximum process rate of the centrifuge. Typically the operator will most likely set the feed rate at a much lower than optimal rate “safe rate” to ensure the centrifuge does not trip on overload. If the centrifuge does trip on overload it will be “plugged” and will require a great deal of effort to “unplug.” There will be down time associated with this event and loss of revenue.
There are devices that are available which will sense the load on the planetary gearbox and shut the feed pump off if an overload is imminent. These devices are intended to protect the centrifuge from “plugging” by shutting off the feed pump, but do not control or adjust the feed rate to allow the centrifuge to continue processing. Additionally, these systems utilize expensive load cells and the centrifuge over torque device must be modified to accept the load cell.
Thus there remains a need for a simple inexpensive device, which can be easily retrofit without modification to a standard fixed drive centrifuge, that will provide for automatic control of the centrifuge feed rate to ensure optimal process rate.